A case study of the influx of upper mantle fluids into the crust

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• 作者：Zhang ; Ronghua ; Hu ; Shumin
• 关键词：CO₂-bearing aqueous fluids ; phase separation ; gold ; oil ; gas field ; basaltic rocks ; upper mantle fluids
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2002
• 出版时间：November 30, 2002
• 年：2002
• 卷：118
• 期：3-4
• 页码：319-338
• 全文大小：883 K

文摘

Geochemical and geophysical investigations in the Bohai Gulf and adjacent areas, China, indicate that uplift of the high-conductivity layer in the lithosphere coincides with the area of high heat flow. In this area are distributed abundant oil and gas fields in a Tertiary fault basin and also large quantities of basaltic rocks. Gas fields, mostly CO₂ bearing, occur at the basin margins, where a widespread alkaline olivine basalt has high contents of gold. Geochemical prospecting of the surface (soil and soil gas) in the area indicates that there is an anomaly zone of large-scale gold mineralization, and large gold deposits have been found in this area. Isotopic study demonstrates that CO₂ in the volcanic rocks and in the CO₂-bearing gas deposits are all derived from the mantle. Experiments show that Au- and CO₂-bearing hydrothermal fluids separated into vapor phase and liquid phases respectively due to a reduction of pressure and temperature over the temperature range from 250 to 290°C and at 22 M Pa. Au appears in the vapor phase rich in CO₂. That proves that it is possible that CO₂-bearing aqueous fluids (in gas phase) can carry gold and transport it from deeper parts of lithosphere to the surface.